Telescopic position adjustment mechanisms for adjusting the telescopic position of a telescoping element relative to a base and maintaining the telescoping element in the selected position are well known.
One type of telescopic position adjustment mechanism relies on a support reservoir disposed between the telescoping element and the base for supporting the telescoping element against the base. In this type of telescopic position adjustment mechanism, the telescoping element is slidably received within the base or vice versa, and the support reservoir is in valve-governed fluid communication with a sink reservoir, each of which contains an incompressible fluid. By opening the valve, the position of the telescoping element relative to the base can be adjusted. Moving fluid from the support reservoir to the sink reservoir will telescopically collapse the telescoping element, and moving fluid from the sink reservoir to the support reservoir will telescopically extend the telescoping element. This type of telescopic position adjustment mechanism is often used as an adjustable seat post for a bicycle seat.
One problem with the above-mentioned telescopic position adjustment mechanism is that the position adjustment is imprecise. For example, if the above-mentioned telescopic position adjustment mechanism is used to support a bicycle seat, a rider who wishes to lower the seat only slightly from its current position may open the valve between the support reservoir and the sink reservoir for too long. If the rider is applying his or her weight to the seat, this can cause the seat to collapse beneath the rider, which is inconvenient.
Another difficulty with the above-mentioned telescopic position adjustment mechanism is rotation of the telescoping element relative to the base. Although there are a number of rotation resistance mechanisms, such as tongue and groove arrangements and using polygonal rather than cylindrical shapes for the telescoping element and base, because the telescoping element is slidably received within the base or vice versa, there must be sufficient play between the telescoping element and the base to enable one to slide freely relative to the other and prevent frictional jamming. Moreover, this play increases as the rotation resistance mechanisms become worn with use. The play between the telescoping element and the base has the undesired consequence of permitting rotation of the telescoping element relative to the base. Even if angularly small, such rotation can become a noticeable and discomfiting “wobble” when the above-mentioned telescopic position adjustment mechanism is used to support a bicycle seat.